Turbocharger, notably for a combustion engine

ABSTRACT

The turbocharger comprises a shaft  14 , a housing  12 , a turbine wheel  20  and a compressor wheel  22  mounted onto the shaft, and at least a rolling bearing  18  disposed between the shaft and the housing and comprising an inner ring  26 , an outer ring  28  and at least one row of rolling elements  30  disposed into a rolling space  40  defined between the rings. A damping space  38  is defined between an outer surface  28   a  of the outer ring and a bore  16  of the housing inside which a lubricant is located.

CROSS-REFERENCE

This application claims priority to European Patent Application No.EP11305761.6 filed on Jun. 17, 2011.

FIELD OF THE INVENTION

The present invention relates to the field of turbochargers, and inparticular those used in combustion engines for automotive vehicles.

BACKGROUND OF THE INVENTION

In such application, a turbocharger is used to enhance the combustionengine performance by blowing compressed air into the cylinders of saidengine.

A turbocharger generally comprises a housing, a shaft extending throughan opening formed on the housing, a turbine wheel mounted on a first endportion of the shaft and located in an exhaust gases passage of thecombustion engine, a compressor wheel mounted on an opposite second endportion of said shaft and located in an admission gases passage of theengine, and rolling bearings disposed between the shaft and the housing.When the turbine wheel is rotated by the flow of the exhaust gases, theshaft and the compressor wheel are rotated which leads to a compressionof the admission gases introduced into the cylinders of the combustionengine.

The engine oil may be used for the lubrication of the rolling bearings.However, when the combustion engine stops, the delivery of engine oil isshut off. This causes a strong temperature increase of the residual oillocated between the shaft and the rolling bearing near to the turbinewheel. The cooling of said rolling bearing is thus not satisfactory.Otherwise, the engine oil may contain foreign matter, for example smallmetal particles, thereby causing a premature wear of the rollingbearings.

To overcome these drawbacks, European patent application EP-A2-2 042 758discloses a turbocharger comprising a tank for storing a specificlubricating oil for the rolling bearings, said tank being formed withinthe housing. A tube is provided between the storage tank and the spacewhere are housed the rolling bearings to supply by capillary action thelubricating oil. In the disclosed turbocharger, an intermediate bearingcasing is also mounted between the rolling bearings and the housing,said casing being equipped with damper rings to reduce the transmissionof vibrations emitted by the turbine and compression wheels.

This leads to a complex structure of the turbocharger as well as anincrease of the mounting cost.

One aim of the present invention is therefore to overcome theaforementioned drawbacks.

SUMMARY OF THE INVENTION

It is a particular object of the present invention to provide aturbocharger which is simple to manufacture and economic, whileguaranteeing good sealing and damping properties.

In one embodiment, the turbocharger comprises a shaft, a housing, aturbine wheel and a compressor wheel mounted onto the shaft, and atleast a rolling bearing disposed between the shaft and the housing andcomprising an inner ring, an outer ring and at least one row of rollingelements disposed into a rolling space defined between the rings. Adamping space is defined between an outer surface of the outer ring anda bore of the housing inside which a lubricant is located.

In one embodiment, the turbocharger further comprises at least twosealing means closing at least the rolling space.

In one embodiment, the turbocharger further comprises at least twosealing means closing the damping space and the rolling space.

In one embodiment, the turbocharger further comprises passage means forthe lubricant putting the damping space and the rolling space intocommunication.

In one embodiment, the sealing means are axially offset outwards withrespect to the passage means.

The passage means may comprise a gap between the outer ring and thehousing. Alternatively or in combination, the passage means compriseholes made in the thickness of the outer ring. The lubricant locatedinside the damping space may be grease.

In one embodiment, the sealing means are disposed radially between theshaft and the housing.

In another embodiment, the sealing means are disposed radially betweenthe inner and outer rings. The sealing means may only close the rollingspace. The rolling space may be filled with a lubricant distinct fromthe lubricant located in the damping space.

In one embodiment, the axial length of the rolling bearing rangesbetween 30% and 95% of the axial dimension of the housing, andpreferably ranges between 70% and 80%.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The present invention and its advantages will be better understood bystudying the detailed description of specific embodiments given by wayof non-limiting examples and illustrated by the appended drawings onwhich:

FIG. 1 is an axial section of a turbocharger according to a firstexample of the invention, and

FIG. 2 is an axial section of a turbocharger according to a secondexample of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As illustrated on the FIG. 1, which illustrates an embodiment of aturbocharger 10 according to an example of the invention, theturbocharger comprises a housing 12, a shaft 14 extending along alongitudinal axis 14 a through a cylindrical bore or opening 16 of thehousing, a rolling bearing 18 mounted onto the shaft 14 and disposedinto the bore 16, a turbine wheel 20 fixed at one end of the shaft 14and a compressor wheel 22 fixed at an opposite end of said shaft. Thehousing 12 comprises a cap 24 fixed at one axial end. In the disclosedembodiment, the axial length of the rolling bearing 18 ranges between60% and 90% of the axial dimension of the bore 16 of the housing, andmore precisely between 70% and 80%.

The rolling bearing 18 comprises an inner ring 26 and an outer ring 28between which are housed two rows of rolling elements 30 and 32, whichin this case are balls, and two annular cages 34, 36 respectivelymaintaining the circumferential spacing of the rolling elements 30, 32.The axis 18 a of the rolling bearing is coaxial with the axis 14 a ofthe shaft of the turbocharger.

The inner and outer rings 26, 28 are concentric and symmetric withrespect to a transverse radial plane passing through the centre of therolling bearing. The rings 26, 28 are of the solid type. A “solid ring”is to be understood as a ring obtained by machining with removal ofmaterial (by machining, grinding) from metal tube stock, bar stock,rough forgings and/or rolled blanks.

The outer ring 28 comprises an outer cylindrical surface 28 a delimitedby opposite radial lateral surfaces 28 b and 28 c, the radial surface 28c axially come into contact with a radial shoulder of the housing 12.The outer ring 28 also comprises a bore 28 d of cylindrical shape fromwhich are formed toroidal raceways (not referenced) having incross-section a concave internal profile adapted to the rolling elements30, 32. The raceways are symmetrical with respect to the transverseradial plane passing through the centre of the rolling bearing.

An annular radial gap or space 38 exists between the outer surface 28 aof the outer ring and the bore 16 of the housing. The annular space 38is delimited radially by the outer ring 28 and the bore 16 of thehousing, and axially by the radial shoulder of said housing and the cap24. An annular axial space or gap 39 is defined between the radialsurface 28 b of the outer ring and the cap 24.

In the disclosed embodiment, the inner ring 26 is made in two partswhich are identical, symmetrical with respect to the transverse radialplane of symmetry of the rolling bearing and mounted axially fixedly oneagainst the other. The inner ring 26 is here composed of two identicalhalf-rings.

Alternatively, the inner ring may be made into one part. The inner ring26 has a bore 26 a of cylindrical shape into which the shaft 14 ismounted. Said bore is delimited by opposite radial lateral surfaces 26 band 26 c, which are respectively coplanar with the lateral surfaces 28b, 28 c of the outer ring. The radial surface 26 c axially bears againsta radial shoulder of the shaft 14. The inner ring 26 also comprises anexterior cylindrical surface 26 d onto which first and second toroidalcircular raceways (not referenced) are formed. The said raceways have incross-section a concave internal profile adapted to the rolling elements30 and 32, the said raceways being directed radially outwards. Theraceways are symmetrical with respect to the transverse radial planepassing through the centre of the rolling bearing.

An annular rolling space 40 is defined between the inner and outer rings26, 28 in which the rolling elements 30, 32 and the associated cages 34,36 are housed. The rolling space 40 is delimited radially by theexterior surface 26 d of the inner ring and the bore 28 d of the outerring, and axially by the radial surfaces 26 b, 28 b and 26 c, 28 c ofsaid rings.

The turbocharger 10 is further provided with a sealing ring 42 mountedradially between the shaft 14 and the cap 24 and axially disposedbetween the compressor wheel 22 and the rolling bearing 18, and with anannular sealing ring 44 disposed radially between the shoulder of saidshaft 14 and the bore 16 of housing and axially mounted between therolling bearing 18 and the turbine wheel 20. The sealing ring 42 islocated axially between the radial surfaces 26 b, 28 b of the inner andouter rings and the compressor wheel 22, the sealing ring 44 beinglocated axially between the radial surfaces 26 c, 28 c of said rings andthe turbine wheel 20. The sealing rings 42, 44 are identical to oneanother and apply a static sealing with the shaft 14 and a dynamicsealing respectively with the cap 24 and the housing 12. The sealingrings 42, 44 are fitted into grooves (not referenced) provided on theexterior surface of the shaft 14, extend radially and respectively comeinto sliding contact with the cap 24 and the housing 12. Alternatively,the sealing rings may remain at a small distance from said cap andhousing. The sealing rings 42, 44 are made from metal, advantageouslyfrom a thin metal sheet blank. Alternatively, the sealing rings may bemade by moulding a synthetic material such as an elastomer. The sealingrings 42, 44 are continuous in the circumferential direction. Tofacilitate there fitting into the grooves of the shaft 14, each of thesealing rings may alternatively be open at a point of its circumference.

The sealing rings 42, 44 close from the outside the rolling space 40 ofthe rolling bearing and the annular space 38 defined between the outerring 28 of said bearing and the bore 16 of the housing. A singlelubricant 46, such as grease, may be used to fill the annular radialspaces 38, 40. The lubricant 46 disposed into the radial space 38 mayenable to damp the vibrations emitted by the rotation of the turbine andcompressor wheels 20, 22. The transmission of the vibrations emitted bysaid wheels to the housing 12 may be limited. The radial space 38 filledwith lubricant 46 acts as a damping space. The damping space 38communicates with the rolling space 40 via the axial annular gap 39defined between the outer ring 28 and the cap 24. Said gap 39 formspassage means for the lubricant 46 communicating with the damping space38 and the rolling space 40. The sealing ring 42, 44 have a dualfunction, namely to preventingress of undesirable external pollutingelements into the rolling bearing 18 and to keep the lubricant 46 intothe damping space 38 and the rolling space 40. The lubricant 46 isintroduced during the assembly of the turbocharger.

In the disclosed embodiment, the axial gap 39 for the lubricant enablesto put the damping space 38 and the rolling space 40 into communication.Alternatively or in combination, it could also be possible to maderadial through-holes in the thickness of the outer ring 28 to formpassage means for the lubricant between the damping space 38 and therolling space 40.

The embodiment shown on FIG. 2, in which identical parts are givenidentical references, differs from the previous embodiment in that theradial surface 28 b of the outer ring axially comes into contact withthe cap 24 of the housing, and in that the rolling bearing 18 furthercomprises annular sealing rings 50, 52 disposed radially between theinner and outer rings 26, 28. The sealing rings 50, 52 are fitted insideannular grooves (not referenced) formed radially towards the inside fromthe exterior surface 26 d of the inner ring, respectively in thevicinity of the radial surfaces 26 b, 26 c. The sealing rings 50, 52 aresymmetrical with one another relative to the transverse radial plane ofsymmetry of the rolling bearing. Each sealing ring 50, 52 extendsradially towards the outer ring 28 and comes into sliding contact withthe bore 28 d of said ring. Alternatively, the sealing rings may remainat a small distance from said bore. The sealing rings 50, 52 are madefrom metal or from a synthetic material.

The sealing ring 50 is axially situated on the compressor wheel side andthe sealing ring 52 on the turbine wheel side. The sealing ring 50 islocated axially between the row of rolling elements 30 and the radialsurfaces 26 b, 28 b of the inner and outer rings, the sealing ring 52being mounted axially between the row of rolling elements 32 and theradial surfaces 26 c, 28 c of said rings. In this embodiment, therolling space 40 inside which are housed the rolling elements 30, 32 andthe cages 34, 36 is axially delimited by the radial sealing rings 50,52. The closed rolling space 40 is filled which a lubricant 54, such asgrease. The lubricant 54 may be distinct from the lubricant 46 used intothe damping space 38. The sealing rings 50, 52 only close the rollingspace 40, the damping space 38 being closed by the outer ring 28, thehousing 12 and the cap 24. The damping space 38 and the rolling space 40are not in communication with one another.

In another embodiment, with such sealing rings 50, 52 and the axialcontact between the radial surface 28 b of the outer ring and the cap24, it could also be possible to made radial through-holes in thethickness of said outer ring axially between the rows of rollingelements 30, 32 to obtain passage means for the lubricant putting thedamping space 38 and the rolling space 40 into communication. In thiscase, the sealing rings close the two spaces 38, 40 and the lubricant46, 54 is the same for both spaces.

In another variant, the turbocharger 10 may be not provided with sealingrings 42, 44, 50, 52 and the rolling bearing 18 is directly lubricatedby the engine oil.

It should be noted that the embodiments illustrated and described weregiven merely by way of non-limiting indicative examples and thatmodifications and variations are possible within the scope of theinvention. The invention applies not only to turbocharger comprising anangular contact ball rolling bearing with a double rows of balls butalso to turbocharger comprising other types of rolling bearing, forexample rolling bearing having four points contact and/or with a singlerow of balls or with at least three rows of balls.

Furthermore, the invention applies to rolling bearings comprising aplurality of inner rings and/or a plurality of outer rings. Finally, ithas to be made clear that by a turbocharger it is also meant a wasteheat recovery turbine, a turbo-compound or a compressor.

1. A turbocharger comprising; a shaft (14), a housing (12), a turbinewheel (20) and a compressor wheel (22) mounted onto the shaft, and atleast a rolling bearing (18) disposed between the shaft and the housingand comprising; an inner ring (26), an outer ring (28) and at least onerow of rolling elements (30) disposed into a rolling space (40) definedbetween the rings, and wherein a damping space (38) is defined betweenan outer surface (28 a) of the outer ring and a bore (16) of the housinginside which a lubricant is located.
 2. The turbocharger according toclaim 1, further comprising at least two sealing means (42, 44; 50, 52)closing at least the rolling space (40).
 3. The turbocharger accordingto claim 2, wherein the sealing means (42, 44) close the damping and therolling spaces.
 4. The turbocharger according to claim 2, wherein thesealing means (42, 44) are disposed radially between the shaft (14) andthe housing (12).
 5. The turbocharger according to claim 2, wherein thesealing means (50, 52) are disposed radially between the inner and outerrings.
 6. The turbocharger according to claim 5, wherein the sealingmeans (50, 52) only close the rolling space (40).
 7. The turbochargeraccording to claim 6, wherein the rolling space (40) is filled with alubricant distinct from the lubricant located in the damping space (38).8. The turbocharger according to claim 1, further comprising passagemeans for the lubricant putting the damping space (38) and the rollingspace (40) into communication.
 9. The turbocharger according to claim 8,wherein the passage means comprise a gap (39) between the outer ring andthe housing.
 10. The turbocharger according to claim 8, wherein thepassage means comprise holes made in the thickness of the outer ring.11. The turbocharger according to claim 1, wherein the lubricant locatedinside the damping space (38) is grease.
 12. The turbocharger accordingto claim 1, wherein the axial length of the rolling bearing (18) rangesbetween 30% and 95% of the axial dimension of the housing (12), andpreferably ranges between 70% and 80%.